The present invention relates to a method for establishing the angular position of a vehicle relative to at least one rotational axis, for example, its longitudinal axis and/or its transverse axis, in which the rotation rate of the vehicle about the rotational axis is detected using at least one rotation rate sensor and the angular position, for example, the roll angle about the longitudinal axis of the vehicle and/or the pitch angle about the transverse axis of the vehicle, is established by integration of the detected rotation rate, with the offset error of the rotation rate sensor being considered.
Rotation rate sensors used as roll rate sensors may be used in connection with airbag control devices for triggering side and head airbags. A corresponding sensor system may also be used for a rollover prevention system.
The output signal of a rotation rate sensor may be affected by an offset error, which may be conditioned by various factors, such as, for example, aging or incorrect adjustment of the sensor. For simple integration algorithms, with which the angular position of the vehicle may be established, the offset error may lead to drift of the integrated rotation rate signal. Therefore, even during long periods of driving straight on level roads, a calculated roll angle may increase to values that may cause incorrect triggering of restraint devices.
It is an object of an exemplary embodiment of the present invention to check the angular position of the vehicle, which is established with the aid of at least one rotation rate sensor, in the course of a plausibility inspection, that is, to check whether an integrated rotation rate signal may reproduce the actual angular position of the vehicle or whether it lies outside an angular range that may be considered for the actual angular position of the vehicle, on the basis of a driving situation.
This object may be achieved by an exemplary embodiment according to the present invention in that, in addition to the rotation rate, transverse acceleration AQ, that is, the acceleration of the vehicle transverse to the rotational axis, may be detected and checked, with reference to the dependence of the actual angular position of the vehicle on transverse acceleration AQ, to determine whether the established angular position corresponds to the actual angular position of the vehicle.
The actual angular position of the vehicle may be dependent on corresponding transverse acceleration AQ and the load state of the vehicle. Since the relationship between transverse acceleration AQ and angular position is not definite, the detection of transverse acceleration AQ may not be sufficient to establish the actual angular position of the vehicle. However, each measured transverse acceleration AQ may be assigned an angular range for the actual angular position of the vehicle that covers all possible load states of the vehicle. The angular range that may be considered for the actual angular position of the vehicle on the basis of transverse acceleration AQ measured in parallel represents an easily established and extremely practical framework for the plausibility check of the angular position that may be established by integration of the rotation rate signal detected and in consideration of the sensor offset. With the aid of such a plausibility check, according to an exemplary embodiment of the present invention, whether the rotation rate integral drifts both during straight driving and during driving around curves may be established.
In the exemplary embodiment according to the present invention, which is believed to be advantageous because it may be relatively xe2x80x9csimplexe2x80x9d to implement, an upper limit value and a lower limit value for the actual angular position are established with reference to the dependence of the actual angular position of the vehicle on transverse acceleration AQ. It is then checked whether the established angular position lies within the interval established by the upper and lower limit values. The angular position that results at a given transverse acceleration AQ at the maximum load state of the vehicle may be selected as the upper and/or lower interval limit, since, in this case, the greatest angles of inclination may be expected. However, the interval limits may be selected more generously, in consideration of possible changes in the offset error.
The relationship between the actual angular position of a vehicle and the corresponding transverse acceleration depends on the respective vehicle type. Sometimes, it may be described well by a linear relationship, so that the interval limits may be established simply by multiplying current detected transverse acceleration AQ by the same factor. If the relationship between the actual angular position and transverse acceleration AQ may not be readily functionally described, corresponding data should be established and made available in the form of characteristic curves by a manufacturer, for example, in the course of driving tests. The limit values for the actual angular position of the vehicle may then be established easily, with the aid of a characteristic curve that reproduces the relationship between the actual angular position and transverse acceleration AQ, during normal driving operation of the fully loaded vehicle.
In an exemplary method according to the present invention, not only is a plausibility check of the established angular position performed using detected transverse acceleration AQ, but also a possibly necessary correction of the established angular position. Thus, it is believed to be advantageous to correct the established angular position, if it exceeds the upper limit value for the actual angular position or falls below the lower limit value for the actual angular position, at a given transverse acceleration AQ. The limit value that the angular position exceeds or falls below, respectively, may be used for correction, for the established angular position.
In another exemplary method according to the present invention, in addition to the plausibility check of the established angular position, a correction of the offset error also occurs if necessary, with transverse acceleration AQ being used as a basis. Thus, correction of the offset error may be necessary, if the established angular position of the vehicle exceeds the upper limit value for the actual angular position or falls below the lower limit value for the actual angular position, at a given transverse acceleration AQ. It is believed to be advantageous if this quasi self-learning correction of the offset error only occurs slowly. For this purpose, the offset error is decremented and/or incremented by a presettable value. The respective currently established offset error is stored so that the current offset error may be taken into consideration, during the establishment of the angular position of the vehicle, with reference to the detected rotation rate and, for example, may also be available when driving is resumed.
Yet another exemplary method according to the present invention may perform a correction of the established angular position independently of a possible correction of the offset error, and the criteria for these two corrections do not have to be identical.